This invention relates to wooden-type truss structures which include upper and lower wooden chords interconnected by webs formed of wooden sheets. Both the chord members and the webs may either be solid wood members or composite or laminated wooden members, as desired. Such truss structures have been constructed extensively in the prior art and are typically characterized by a pair of beams running parallel to one another or angled relative one another to form a roof incline, with the webs spanning these chords in a plane intersecting both chord axes. As has been recognized by the prior art, the greatest difficulty encountered in the construction of such truss structures is the web/chord joint formed at the cord groove. Enough of the web cross-section must remain at the joint to prohibit shear forces from rupturing the web member adjacent the chord. At the same time, however, the joint must provide substantial surface interface for gluing purposes. In addition, it is preferable that these desirable objects be accomplished without a requirement for long duration clamping devices to maintain alignment of the structures during curing of the adhesive used for their interconnection.
In the prior art, it has been shown that it is possible to increase the surface area of glue contact by grooving the web member to provide multiple grooved interconnections between the web member and each of the chords. Such an attempted solution is shown, for example, in U.S. Pat. No. 4,074,498, in U.S. Pat. No. 3,991,535, and in U.S. Pat. No. 3,960,637. Unfortunately, these attempted solutions substantially increase the cost of fabrication, since additional grooving and additional fitting of grooves, all requiring close tolerance mill work, are required. Of even more importance is the fact that increased surface area at the glue joint is provided only at the expense of a lack of sheer strength at the web/chord interface, since the cross-section of the web is typically substantially reduced by internal grooves near the interface, so that the structural integrity of the web itself is degraded.
Other solutions to the problem have suggested a compression of the web at its edges and the placement of the compressed or tapered edges into tapered grooves to provide self-pressurizing joints as the wood, which has been previously compressed, expands in response to the glue's moisture. Unfortunately, this solution, as presented in U.S. Pat. No. 3,490,188, for example, does not provide adequate venting for glue. Thus, if the groove in the chord is partially filled with glue, the web will often not completely enter the groove, even under pressure, since the glue cannot be vented from the groove during assembly. Furthermore, even if all of the glue is vented, it is unlikely, using the system of that patent, that the glue will be evenly vented to assure coating of all of the interface surfaces. Rather, the glue tends to vent from portions having softer wood surfaces or indentations, finding a single path of least resistance, so that much of the surface area may remain uncoated and therefore not contribute to the structural integrity of the joint.
In the prior art, the edges of the web in above configurations, whether they were tapered edges or multiple grooved interconnections, have always been machined or compressed along the longitudinal dimension of the web. This was done because such forming of the wood of the web was easier and it facilitated the handling of the workpiece.
In the prior art is has been thought necessary to use configurations, such as those described above, in order to pressurize and align the joint interface without external clamps. Thus, it has been thought necessary to either risk the loss of a shear strength at the joint or to risk poor adhesive coverage at the joint in order to bond the structure without clamps which remain in place during the assembly and curing processes.